Influence Of Coupling Beam Axial Restraint On Analysis And Design Of Reinforced Concrete Coupled Walls

Reinforced concrete coupled shear walls are effective systems for resisting lateral loads, often used in mid to high-rise buildings in earthquake-prone areas. These walls usually feature openings for doors and windows, dividing a solid wall into two separate piers. The strength of these walls comes not just from the sum of two individual piers, but from wall piers cross-section and the framing action between the wall piers through the coupling beams. In an earthquake, coupling beams serve as fuse elements, distributing seismic energy throughout the height of the building. This not only reduces the bending stress at the base of the shear walls but also improves their overall strength, stiffness, and resistance to lateral forces. Properly designed coupling beams, with sufficient longitudinal, diagonal, and confinement reinforcement, can effectively absorb energy while maintaining significant strength and stiffness, even under large deformations.The objective of this study was to develop, calibrate, and validate a new coupling beam model that integrates axial and lateral interactions under cyclic loading conditions. This model aims to reliably predict the elastic and inelastic responses of diagonally reinforced coupling beam elements. The proposed analytical model incorporates a fiber-based concrete cross-section, and diagonal trusses to account for axial interactions between the nonlinearity in the steel and concrete along the beam's length. This feature allows the model to capture additional axial force developed in the element due to the axial restraint from the wall piers, thereby increasing or decreasing the lateral strength of the beam. Additionally, the model includes the slip-extension behavior between the coupling beam and the supporting wall through zero-length fiber-based elements at both ends of the beam. Finally, with the development of the new analytical model and recent advancements in understanding the shear strength of RC shear walls, a new coupled/core wall design approach has been introduced to optimize the design of RC core walls. A variety of archetypes have been designed, based on both current design practices and the proposed approach. Detailed analytical models have been developed, and the efficiency of the proposed design has been evaluated through nonlinear static and dynamic analyses. To conduct the dynamic analysis, suites of ground motions were selected using the CMS approach and scaled to the MCER level of hazard. It has been demonstrated that the designed archetypes based on proposed procedure provide a more reliable shear responses under seismic loading compared to current design practices.